This invention relates generally to modular prosthesis and more particularly to modular prosthesis having a plurality of distal components adapted to be mounted to a proximal component with a locking nut.
In many total joint devices, longer stems are employed in either more difficult cases or cases with abnormal anatomy. A distally modular stem is desirable since it allows positioning of the distal stem consistent with the patient's anatomy while independently positioning the proximal body in order to optimize the biomechanics. Firm locking of the proximal body and distal stem is critical to the success of such a modular stem. Two critical concerns to clinicians are that the components could disassociate or fracture in vivo.
Many modular prosthetic systems are available that couple a distal stem to a proximal component. Often this coupling is accomplished using a Morse-type taper joint with the frusto-conical male portion of the joint being formed on one component while the female frusto-conical cavity is formed on the other component. In several such devices a fastener is utilized to aid the taper joint in remaining associated in vivo.
U.S. Pat. No. 6,090,146 discloses a male/female connecting joint between an implant body component and a stem component with a fastener that engages the implant components and draws them together. Thus, the device disclosed therein attempts to address concerns about disassociation of the implant components in vivo. However, the device disclosed therein does not fully address the risk of fracture in vivo.
Often the fasteners utilized to couple components of modular prosthesis together are configured to non-uniformly transfer stresses experienced by the fastener to the adjacent prosthesis components. Typically such fasteners are inserted into a nut receiving-cavity that has a flat bottom surface. When a standard locking nut is screwed onto a threaded shaft disposed in such a cavity, the nut (when the device is under stress) may contact the bottom surface of the cavity at a single point resulting in the stresses being non-uniformly transferred. This non-uniform distribution of stresses may induce the prosthesis components to fracture under stress. Thus, a fastener for securing the components of a modular prosthesis together which addresses both the concerns of disassociation and fracture of the components in vivo would be appreciated.
The disclosed modular prosthesis components and locking nut therefor address the concerns regarding disassociation and fracture of prosthesis components in vivo. The disclosed modular prosthesis components utilize a locking nut received in a cavity in one component of the prosthesis which is secured to the threaded shaft of the other component of the prosthesis to inhibit disassociation of the prosthesis components. The locking nut and cavity are formed to engage each other in multiple locations when the locking nut is tightened to address concerns regarding fracture of the prosthesis components.
According to one aspect of the invention, a modular prosthesis is provided that includes a first prosthesis component, a second prosthesis component and a locking nut. The first prosthesis component is configured to include a first half of a male/female connecting joint and a threaded shaft configured to receive the locking nut thereon. The second prosthesis component is formed to include a second half of a male/female connecting joint, a cavity configured to receive the locking nut therein and a bore communicating with the cavity and the second half of the male/female connecting joint and sized to receive the threaded shaft therethrough. The nut-receiving cavity is formed to include a shaped bottom surface through which the bore extends. The locking nut is formed to include a distal end having a shape configured to cooperate with the shaped bottom surface of the nut receiving cavity to create multiple locations of engagement. The threaded shaft, locking nut, bore and cavity are configured so that when the locking nut is tightened onto the threaded shaft the distal end of the locking nut is urged into engagement in multiple locations with the bottom surface of the cavity.
According to another aspect of the invention, a modular prosthesis is provided that includes a first prosthesis component, a second prosthesis component and a locking nut. The first prosthesis component is configured to include a mating surface and a threaded shaft extending from the mating surface and configured to receive the locking nut thereon. The second prosthesis component is formed to include a mating surface, a cavity configured to receive the locking nut therein and a bore communicating with the cavity and the mating surface and sized to receive the threaded shaft therethrough. The nut receiving cavity is formed to include a shaped bottom surface through which the bore extends. The locking nut is formed to include a distal end having a shape configured to cooperate with the shaped bottom surface of the nut-receiving cavity to create multiple locations of engagement. The threaded shaft, locking nut, bore and cavity are configured so that when the threaded shaft of the first prosthesis extends through the bore and the locking nut is tightened onto the threaded shaft the distal end of the locking nut is urged into engagement in multiple locations with the bottom surface of the cavity and the mating surfaces of the first and second components are urged into engagement.
According to yet another aspect of the invention, a modular prosthesis includes a distal prosthesis component, a locking nut and a proximal prosthesis component. The distal prosthesis component is configured to include a male joint component, a threaded shaft, a stem and an axis. The male joint component and threaded shaft are formed concentrically about the axis. The threaded shaft extends proximally from the male joint component and the stem extends distally from the male joint component. The locking nut is configured to be received on the threaded shaft and formed to include a radiused distal end exhibiting a radius of curvature. The proximal prosthesis component comprises a body having a longitudinal axis. The body is configured to include a female joint component configured to mate with the male joint component, a nut-receiving cavity and a shaft-receiving bore formed concentrically about the longitudinal axis. The nut-receiving cavity is configured to receive the locking nut therein and includes a radiused bottom surface exhibiting a radius of curvature configured to cooperate with the radiused distal end of the locking nut to create multiple locations of engagement. The bore is sized to receive the threaded shaft therein and communicates with the nut-receiving cavity through the radiused bottom surface and the female joint component. The threaded shaft, locking nut, bore and cavity are configured so that when the locking nut is tightened onto the threaded shaft the radiused distal end of the locking nut is urged into engagement in multiple locations with the radiused bottom surface of the cavity. A plurality of such proximal prosthesis components having differently sized bodies but similarly sized female joint components may be provided. A plurality of such distal prosthesis components may be provided having differently sized stems but similarly sized male joint components. A plurality of such locking nuts may be provided having different lengths but similar diameters.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.